When you see the error “Mounting failed. See log file for details.”, please look inside the log file for errors.
If your vault is located on a WebDAV share and you mounted this share using gvfs (this is the standard in most Linux systems when you use the default file browser), unlocking a vault may fail.
If you have this problem the logfile will contain something like
/run/user/1000/gvfs/dav:host=localhost,port=46111,ssl=false,prefix=%2Ftest/test2/masterkey.cryptomator: Operation not supported
The problem is caused by an upstream bug in the JDK, as described here.
A workaround is to mount the share using:
mount -t davfs -o uid=username http://host:port/path /user/chosen/directory
Please note that username is your username on your linux system in this case - not the username you use to login on the WebDAV server.